Fujisaki S
Department of Pediatrics, Hokkaido University School of Medicine, Sapporo, Japan.
Hokkaido Igaku Zasshi. 2000 Jan;75(1):45-52.
Osteopontin, a secreted acidic phosphoglycoprotein with calcium binding activity, has been reported to have diverse functions, including cell adhesion, calcium remodeling, cell signaling and cellular transformation. This recalls us to a concept that the osteopontin can be a marker for certain clinicopathological states. However, a method for analysis of osteopontin has not successfully been developed to be utilized. We have isolated osteopontin from human milk, prepared antibodies specific to it, and tried to establish an enzyme immunoassay (EIA) system to determine osteopontin in serum. It was found that serum osteopontin but not milk osteopontin showed paradoxical phenomena in reaction with the antibodies, i.e., no detectable reaction in immunoelectrophoresis and in EIA, but showing positive reaction in Western blot and in inhibition tests. Taking these phenomena and other circumstantial evidence into account, it was concluded that the serum osteopontin had high molecular fragility, fragmenting into small peptides with paucity of epitopes during incubation time. These findings indicate the possible presence of osteopontins with different molecular characteristics among tissues, and that these characteristics of osteopontin will interfere with the development of quantitative assay.
骨桥蛋白是一种具有钙结合活性的分泌型酸性磷酸糖蛋白，据报道它具有多种功能，包括细胞黏附、钙重塑、细胞信号传导和细胞转化。这使我们想到一个概念，即骨桥蛋白可能是某些临床病理状态的标志物。然而，尚未成功开发出一种可用于分析骨桥蛋白的方法。我们已从人乳中分离出骨桥蛋白，制备了针对它的抗体，并试图建立一种酶免疫测定（EIA）系统来测定血清中的骨桥蛋白。结果发现，血清骨桥蛋白而非乳骨桥蛋白在与抗体反应时表现出矛盾的现象，即在免疫电泳和EIA中无可检测到的反应，但在蛋白质印迹法和抑制试验中呈阳性反应。考虑到这些现象和其他间接证据，得出的结论是血清骨桥蛋白具有高分子脆性，在孵育期间会断裂成表位稀少的小肽。这些发现表明不同组织中可能存在具有不同分子特征的骨桥蛋白，并且骨桥蛋白的这些特征会干扰定量测定方法的开发。
